Question

the first and the last term of a geometric progression is equal to -8 and 1 respectively. If the sum of all the terms is -5, find the number of terms.

Answer 1

First term of the geometric progression (a ) = - 8.

Last term of the geometric progressin  .

Substitute a = - 8 in .

.

Sum of geometric progression .

Substitute a = - 8 and in .

.

To find n, substitute the value r = - 1 / 2 in .

 

⇒ n = 4.

Therefore, the number of terms of the geometric progression is 4.